Environmental influences in cancer aetiology

Purpose. The purpose of this review is to inform both scientists and clinicians about the increase in cancer incidence throughout the Western World and to discuss environmental influences in cancer aetiology, in order to stimulate thoughts about plausible aetiological mechanisms and possible preventative measures.Design. Literature review.Materials and methods. This review was conducted by searching biomedical databases such as PubMed and Medline. Further research to obtain cancer incidence data involved accessing UK cancer registries, major cancer charities and government statistical records from the Office of National Statistics, the Department of Health, and the Department of Environment, Food and Rural Affairs.Results. Cancer incidence rates have increased in the Western World and this increased incidence affects the whole age spectrum. Epidemiological studies have provided some evidence of an association between exposure to environmental contaminants such as organochlorines and increased cancer risk. However, many epidemiological studies have been inconclusive. Similar reviews concerning environmental influences in cancer aetiology concluded that exposures to carcinogenic or endocrine‐disrupting chemicals exist at concentrations too low or have carcinogenic potential too weak to be considered a major factor in cancer aetiology. However, animal and in vitro studies together with epidemiological evidence discussed in this review would dispute that claim; even if healthy adults are not at risk, it would seem that the developing foetus, infant, child and young adults are at risk. In addition, studies discussed in this review show that low oestrogenic potency cannot be used as a marker of the capability of a chemical to cause oestrogenic responses and endocrine disruption. Genetic polymorphisms, which can predispose people to cancer, may interact with environmental contaminants such as organochlorines and endocrine disrupters, thus providing a modifying effect. Prevention measures have hitherto predominately centred on tobacco smoking cessation and diet education. Anecdotal evidence from practising physicians in pre‐industrial and traditional living societies, i.e. Canadian Inuits and Brazilian Indians suggests malignant disease was rare. A relatively new theory other than the somatic mutation theory has been proposed, the main premise being that carcinogenesis is a problem of tissue organization, comparable with organogenesis.Conclusions. It is feasible that chemical environmental contaminants, in particular synthetic pesticides and organochlorines with endocrine‐disrupting properties, could be major factors in cancer aetiology, particularly for hormone‐dependent malignancies, such as breast, testicular and prostate cancers. Animal and in vitro studies provide good evidence of a feasible mechanism whereby environmentally relevant levels of organochlorines and substances of low oestrogenic potency can cause endocrine disruption and consequently malignant disease. In addition, low oestrogenic potency should not be used as a marker of the capability of a chemical to cause oestrogenic responses and endocrine disruption. Preventative measures other than education about tobacco, diet and the promotion of physical activity should be considered. Moreover, it seems to be the most vulnerable members of society: the developing foetus, the developing child and adolescent and the genetically predisposed, who are at risk of developing cancer following involuntary exposure to environmental contaminants. This may be an appropriate time for governments to adopt the precautionary principle until substances to which members of society are involuntarily exposed are proved safe from long‐term, low‐level effects on human health. The World Health Organization estimates that between 1 and 5% of malignant disease in developed countries is attributable to environmental factors: it is possible that this figure may be underestimated. Anecdotal evidence suggests that cancer may be a disease of industrialization. Further research into the tissue organization field theory may be warranted, as some forms of pre‐malignant states are attributed to dysorganogenesis, for example an undescended testis.

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